JP2007193852A - Hologram recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hologram recording medium, which can quickly achieve a plurality of hologram recording operations in stable recording and reproducing. <P>SOLUTION: A hologram recording medium records or reproduces information by irradiation with light. It comprises a hologram recording layer to store the optical interference pattern of the coherent reference light and signal light components in diffraction grating, a reflection layer stacked on the other side of the light incident side of the hologram recording layer, and non-reflecting sections arranged on the reflection layer with the same interval as the recording interval of the diffraction grating. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a record carrier on which information is recorded or reproduced optically, such as an optical disk and an optical card, and more particularly to a hologram record carrier having a hologram recording layer capable of recording or reproducing information by irradiation with a light beam.

  Holograms that can record two-dimensional data at high density are attracting attention for high-density information recording. The feature of this hologram is that the wavefront of light carrying recorded information is recorded as a change in refractive index in volume on a recording medium made of a photosensitive material such as a photorefractive material. By performing multiplex recording on the hologram record carrier, the recording capacity can be dramatically increased. Multiplex recording includes angle multiplexing, phase encoding multiplexing, and the like, and information can be multiplexed and recorded even in the superimposed hologram region by changing the incident angle and phase of the interfering light wave. For example, a hologram recording system has been developed that uses a hologram record carrier with a reflective film laminated as a disk (see Patent Document 1).

  In such a hologram recording system, the reference light should pass through the hologram recording layer and converge as a spot on the reflecting film, and the reference light reflected by the reflecting film should diverge and pass through the recording layer and be recorded at the same time. An information light beam carrying information is passed through the recording layer. Thereby, the reflected reference light and information light interfere in the recording layer to form an interference pattern, and a hologram is recorded in a volume in the recording layer. The hologram having the interference pattern is recorded adjacent to the recording layer so as to sequentially overlap, and the recorded light is reproduced by detecting and demodulating the reproduction light reconstructed from each hologram by irradiating the reference light.

  In a hologram recording system in which the reference light and the information light are incident coaxially from the same side, it is difficult to separate the reference light reflected by the reflective film and the reproduction light from the hologram at the time of information reproduction. For this reason, the read performance of the reproduction signal is deteriorated.

In order to solve this problem, in the hologram recording system disclosed in Patent Document 1, the pupil is divided into two immediately before the objective lens, and the two optical rotators (2 A split optical rotation plate) is arranged to prevent the reference light from entering the photodetector.
Japanese Patent Laid-Open No. 11-311937.

  However, in the conventional method, at the time of recording and reproduction, the two-part optical rotatory plate and the objective lens must be driven integrally. Another problem is that the recording characteristics from the reproduction light corresponding to the vicinity of the division boundary of the two-divided optical rotatory plate are deteriorated.

  When recording a hologram on such a reflection type hologram record carrier, four holograms are recorded by the interference of the incident reference light, the signal light, the reflected reference light, and the four light beams of the signal light. The performance of was uselessly.

  Further, at the time of reproducing information, the reference light is reflected by the reflection film of the hologram record carrier, so that it is difficult to separate it from the diffracted light from the reproduced hologram. For this reason, the read performance of the reproduction signal is deteriorated. Further, since the hologram of the reflected image is recorded, the reproduction signal is deteriorated.

  Therefore, the problem to be solved by the present invention includes, as an example, providing a hologram record carrier, a recording / reproducing method, and a hologram apparatus that enable stable recording or reproduction.

The hologram record carrier according to claim 1 is a hologram record carrier on which information is recorded or reproduced by light irradiation,
A hologram recording layer that stores therein an optical interference pattern by a component of coherent reference light and signal light as a diffraction grating;
A reflective layer laminated on the opposite side of the hologram recording layer from the light incident side;
The reflective layer includes a plurality of non-reflective portions arranged to be equal to the recording interval of the diffraction grating.

  Embodiments of the present invention will be described below with reference to the drawings.

<Hologram record carrier>
Hologram recording / reproduction uses the first light beam of laser light of the same wavelength to perform hologram recording by interference of reference light and signal light, and at the same time, servo-controls the positional relationship between the hologram record carrier and the pickup, particularly the objective lens (focus) In the following description, a servo beam of a laser beam having a wavelength different from that of the first light beam is used for tracking.

  FIG. 1 shows a disc-shaped hologram record carrier 2 on which information is recorded or reproduced by light irradiation, which is an example of this embodiment.

  The hologram record carrier 2 includes a reflective layer 5, a separation layer 6, a hologram recording layer 7, and a protective layer 8, which are laminated on a substrate 3 onto which tracks and the like are transferred from the opposite side of the light irradiation side. Thus, the reflective layer 5 is disposed on the substrate 3 on the side opposite to the light irradiation side of the hologram record carrier. On the reflective layer 5, marks M are formed as non-reflective portions arranged at the same interval as the hologram multiple interval Px. Hologram recording is performed by aligning servo laser light (servo beam SB) substantially coaxial with the first light beam FB for recording on the mark M. This mark may be a pinhole PH (FIG. 1) that transmits the reference light or the light not modulated by the spatial light modulator (0th order light), or does not return the 0th order light beam to the optical axis. It may be a structure like a shape pit (FIG. 2). The pinhole PH may be a hole physically provided in the reflective layer 5 made of a metal reflective film such as aluminum or a dielectric multilayer film, or may be a circular region having a low reflectance at a wavelength used for hologram recording. May be. The diameter of the non-reflective portion such as the pinhole PH is set so as to transmit the reference light or the light not modulated by the spatial light modulator (0th order light). In general, the size of a spot on the Fourier imaging plane determined by the numerical aperture and wavelength of an objective lens used for hologram recording is a guide. As described above, in the present embodiment, the reflection layer 5 transmits the reference light component for hologram recording or reproduction to the back side of the hologram record carrier 2 (so as not to return to the objective lens side), and the non-reflection such as the pinhole PH. The part is formed. Therefore, in order not to return the first light beam FB to the objective lens side, the non-reflective portion is a region having a transmittance with a characteristic value higher than the transmittance of the reflective layer 5 or a characteristic higher than the absorptance of the reflective layer 5. It may be a region having a value absorptance. The characteristic values of the reflectance, transmittance, and absorptance of the non-reflecting portion may be those at the wavelength of the coherent reference light and signal light. For example, the non-reflecting portion reflects at the wavelength of the servo beam SB. The transmittance of the layer 5 may be lower than that of the layer 5. The direction in which hologram recording is sequentially performed along the pinhole PH of the reflective layer 5 is the y direction, the direction perpendicular to the y direction is the x direction, and the pinholes PH are arranged with a pitch Py and a pitch Px.

  The hologram recording layer 7 stores therein an optical interference pattern by the first light beam FB including components of coherent reference light and signal light as a diffraction grating (hologram). The first light beam FB is used so as to include reference light and signal light components for hologram recording at the time of recording. On the other hand, when used for reproduction, the first light beam FB is composed only of reference light components not including signal light components. In the case of phase-encoded multiplex reproduction, the first light beam FB does not include a signal light component, but includes only a phase modulation pattern and a reference light component. A photorefractive material, a hole burning material, a photochromic material, or the like is used as a photosensitive material constituting the hologram recording layer 7 that stores the optical interference pattern.

  For example, a metal film, a phase change film, a dye film, or a combination thereof is used for the reflective layer 5 and is set to reflect the first light beam FB having a wavelength for performing hologram recording. Positioning (focus servo, x, y direction servo) on the hologram record carrier 2 for performing hologram recording is performed by detecting irradiation and reflection of the servo beam SB.

  The substrate 3 is made of, for example, glass, plastic, such as polycarbonate, amorphous polyolefin, polyimide, PET, PEN, PES, or ultraviolet curable acrylic resin, and extends without crossing the main surface. Grooves are formed as a plurality of tracks T. The reflective layer 5 also functions as a guide layer. The separation layer 6 and the protective layer 8 are made of a light transmissive material, and have functions of flattening the laminated structure and protecting the hologram recording layer and the like.

  The servo beam SB is focused to read servo tracks and pits formed on the substrate 3. The pinhole PH may be filled with a material having a characteristic of transmitting the reference light component (0th order light) of the first light beam FB.

  As shown in FIG. 3, a track T equal to the hologram recording interval may be provided between the mark rows (non-reflective portion rows) of the pinhole PH. The track T may be a group shape used in a general optical disc, or may be a region having a different reflectance. The track T on the substrate is provided for at least servo control of the tracking servo. The hologram HG is volume-recorded on the hologram recording layer 7 above the track T. When the substrate 3 is a disk, the track T can be formed spirally or concentrically on the center of the substrate or in a plurality of divided spiral arcs for tracking servo control.

  Servo control uses a light source that emits a light beam and a pickup that includes an optical system that includes an objective lens that focuses the light beam on a track on the reflective layer 5 as a light spot and guides the reflected light to a photodetector. The objective lens is driven by an actuator according to the detected signal. The diameter of the light spot on the reflective layer 5 is a value determined by the light beam wavelength and the numerical aperture (NA) of the objective lens (so-called diffraction limit, for example, 0.82λ / NA (λ = wavelength), but the aberration is the wavelength. If it is sufficiently small as compared with (1), it is set so as to be narrowed down until it is determined only by the wavelength and numerical aperture of the light beam. That is, the light beam emitted from the objective lens is used so as to be focused when the reflective layer 5 is located at the position of the beam waist. The width of the groove is appropriately set according to the output of the photodetector that receives the reflected light from the light spot, for example, a push-pull signal.

  In the above embodiment, the hologram record carrier having the structure in which the reflective layer 5 and the hologram recording layer 7 are laminated via the separation layer is shown, but the separation layer may be omitted. Further, the substrate 3 is disposed between the hologram recording layer 7 and the reflection layer 5 so that the reflection layer 5 is laminated on the opposite side of the substrate 3 on which the hologram recording layer 7 is laminated, and the substrate functions as a separation layer. You can also.

<Hologram device>
FIG. 4 shows an example of a schematic configuration of a hologram apparatus for recording or reproducing information of a hologram record carrier to which the present invention is applied.

  The hologram apparatus of FIG. 4 includes a spindle motor 22 that rotates a disk of the hologram record carrier 2 via a turntable, a pickup 23 that reads a signal from the hologram record carrier 2 by a light beam, and holds the pickup in the radial direction (x direction). Pickup drive unit 24, first light source drive circuit 25a, second light source drive circuit 25b, spatial light modulator drive circuit 26, reproduction light signal detection circuit 27, servo signal processing circuit 28, focus servo circuit 29, x direction A moving servo circuit 30x, a y-direction moving servo circuit 30y, a pickup position detecting circuit 31 connected to the pickup driving unit 24 for detecting a pickup position signal, and a slider servo circuit 32 connected to the pickup driving unit 24 and supplying a predetermined signal thereto. Connected to the spindle motor 22 A rotation number detection unit 33 for detecting a rotation number signal of the pindle motor, a rotation position detection circuit 34 for generating a rotation position signal of the hologram record carrier 2 connected to the rotation number detection unit, and a spindle motor 22 connected to the rotation number detection circuit 34 A spindle servo circuit 35 for supplying signals is provided.

  The hologram hologram apparatus includes a control circuit 37. The control circuit 37 includes a first light source drive circuit 25a, a second light source drive circuit 25b, a spatial light modulator drive circuit 26, a reproduction light signal detection circuit 27, and a servo signal processing circuit. 28, a focus servo circuit 29, an x-direction movement servo circuit 30x, a y-direction movement servo circuit 30y, a pickup position detection circuit 31, a slider servo circuit 32, a rotation speed detection unit 33, a rotation position detection circuit 34, and a spindle servo circuit 35. It is connected. Based on signals from these circuits, the control circuit 37 performs focus servo control relating to the pickup, x and y direction movement servo control, reproduction position (positions in the x and y directions), and the like via these drive circuits. The control circuit 37 is composed of a microcomputer equipped with various memories and controls the entire apparatus. Various control operations are performed according to the operation input by the user from the operation unit (not shown) and the current operation state of the apparatus. It is connected to a display unit (not shown) that generates a control signal and displays an operation status and the like to the user.

  The control circuit 37 executes processing such as encoding of data to be recorded on the hologram input from the outside, and supplies a predetermined signal to the spatial light modulator drive circuit 26 to control the hologram recording sequence. The control circuit 37 restores the data recorded on the hologram record carrier by performing demodulation and error correction processing based on the signal from the reproduction optical signal detection circuit 27. Further, the control circuit 37 reproduces the information data by performing a decoding process on the restored data, and outputs this as reproduced information data.

  5 and 6 show a schematic configuration of the pickup of the hologram apparatus.

  The pickup 23 is roughly divided into a hologram recording / reproducing optical system, a servo system, and a common system, and these systems are arranged on a substantially common plane except for the objective lens OB.

  The hologram recording / reproducing optical system includes a first laser light source LD1, a first collimator lens CL1, a first half mirror prism HP1, a second half mirror prism HP2, a polarization spatial light modulator SLM, a CCD, and a complementary device. A reproduction optical signal detection unit including an image detection sensor CMOS including an array of a metal oxide film semiconductor device, a third half mirror prism HP3, and a fourth half mirror prism HP4.

  The servo system performs diffraction such as a grating that generates a multi-beam for the second laser light source LD2, the second collimator lens CL2, and the servo beam SB for servo-controlling (moving in the xyz direction) the position of the light beam with respect to the hologram record carrier 2. The servo signal detection unit includes an optical element GR, a polarizing beam splitter PBS, a quarter wavelength plate 1 / 4λ, a coupling lens AS, and a photodetector PD.

  The dichroic prism DP and the objective lens OB are a common system.

  As shown in FIGS. 5 and 6, the half mirror surfaces of the first, third, and fourth half mirror prisms HP1, HP3, and HP4 are arranged so as to be parallel to each other and in the normal direction of these half mirror surfaces. The second mirror mirror HP2, the dichroic prism DP, and the polarization beam splitter PBS are arranged so that the half mirror surface and the separation surface are parallel to each other. These optical components are arranged so that the optical axes (one-dot chain lines) of the light beams from the first and second laser light sources LD1 and LD2 extend to the recording and reproducing optical system and the servo system, respectively, and almost coincide with each other in the common system. Has been.

  The first laser light source LD1 is connected to the first light source driving circuit 25a, and its output is adjusted by the circuit so that the intensity of the emitted first light beam FB is strong during hologram recording and weak during reproduction. The second laser light source LD2 is connected to the second light source driving circuit 25b.

  The reflective polarization spatial light modulator SLM has a function of electrically reflecting a part of incident light by a liquid crystal panel having a plurality of pixel electrodes divided into a matrix or the like and transmitting all of the light into a non-reflective state. It has a function. This polarization spatial light modulator SLM is connected to the first light source driving circuit 25a, and is based on page data to be recorded from the spatial light modulator driving circuit 26 (information pattern of two-dimensional data such as bright and dark dot patterns on a plane). The light beam is modulated and reflected so as to have a uniform distribution to generate signal light. When a transmissive liquid crystal panel having a plurality of pixel electrodes divided in a matrix is used as the spatial light modulator instead of the polarization spatial light modulator SLM, it is disposed between the first and second half mirror prisms HP1 and HP2. Is done.

  The reproduction optical signal detection unit including the image detection sensor CMOS is connected to the reproduction optical signal detection circuit 27.

  Further, the pickup 23 includes an objective lens driving unit 36 that moves the objective lens OB in a direction parallel to the optical axis (z direction), a direction parallel to the track (y direction), and a direction perpendicular to the track (x direction). It has been.

  The photodetector PD is connected to the servo signal processing circuit 28, and has, for example, light receiving elements for focus servo and x and y direction movement servo. Output signals such as a focus error signal and a tracking error signal from the photodetector PD are supplied to the servo signal processing circuit 28.

  In the servo signal processing circuit 28, a focusing drive signal is generated from the focus error signal, and this is supplied to the focus servo circuit 29 via the control circuit 37. The focus servo circuit 29 drives the focusing portion of the objective lens driving unit 36 mounted on the pickup 23 according to the drive signal, and the focusing portion adjusts the focal position of the light spot irradiated on the hologram record carrier. To work.

  Further, in the servo signal processing circuit 28, x and y direction movement drive signals are generated and supplied to the x direction movement servo circuit 30x and the y direction movement servo circuit 30y, respectively. The x-direction movement servo circuit 30x and the y-direction movement servo circuit 30y drive the objective lens driving unit 36 mounted on the pickup 23 according to the x and y direction movement drive signals. Therefore, the objective lens is driven by an amount corresponding to the drive current by the drive signals in the x, y, and z directions, and the position of the light spot irradiated on the hologram record carrier is displaced. As a result, the hologram formation time can be ensured by keeping the relative position of the light spot relative to the moving hologram record carrier at the time of recording.

  The control circuit 37 generates a slider drive signal based on the position signal from the operation unit or pickup position detection circuit 31 and the x-direction movement error signal from the servo signal processing circuit 28, and supplies this to the slider servo circuit 32. The slider servo circuit 32 moves the pickup 23 in the radial direction of the disk via the pickup drive unit 24 in accordance with the drive current generated by the slider drive signal.

  The rotation speed detection unit 33 detects a frequency signal indicating the current rotation frequency of the spindle motor 22 that rotates the hologram record carrier 2 on a turntable, generates a rotation speed signal corresponding to the spindle rotation speed, and generates a rotation position. This is supplied to the detection circuit 34. The rotational position detection circuit 34 generates a rotational speed position signal and supplies it to the control circuit 37. The control circuit 37 generates a spindle drive signal, supplies it to the spindle servo circuit 35, controls the spindle motor 22, and rotationally drives the hologram record carrier 2.

  FIG. 7 shows an objective lens driving unit 36 of a pickup for the hologram hologram apparatus of the present embodiment.

  The objective lens driving unit 36 has an actuator base 42 that can vibrate in the y direction by a piezo element 39 coupled to a support unit 38 fixed to a pickup body (not shown). In the pickup body, the above-described required optical components for forming the pickup, such as a rising prism 45 that reflects the light beam from the laser light source at right angles and guides it to the objective lens OB, are provided. The light beam is focused and irradiated as spot light on the information recording surface of the medium on the turntable through the opening 42c and the objective lens OB.

  As shown in FIG. 7, the objective lens OB is formed in a cylindrical shape and is attached to the upper end protruding portion of the lens holder 48 that constitutes a movable optical system together with the objective lens. A focusing coil 50 is wound around the outer periphery of the lens holder 48 so that the center axis of the coil is parallel to the optical axis of the objective lens OB. For example, four tracking coils 51 are attached to the outside of the focusing coil 50 so that the coil central axis is perpendicular to the optical axis of the objective lens OB. Each tracking coil 51 is formed by sticking a previously wound annular shape on the focusing coil 50. The movable optical system composed of the objective lens OB and the lens holder 48 is disposed in a distance from each other in the optical axis direction of the objective lens OB and extends in the y direction perpendicular to the optical axis direction, for a total of four pairs. Is supported by one end of the longitudinal support member 53. However, only three support members 53 are shown in FIG. Each support member 53 is attached to an overhang portion 42 a fixed on the actuator base 42 in a cantilever shape at the other end. Each support member 53 is made of a coil material or the like and has flexibility. The movable optical system including the objective lens OB and the lens holder 48 is movable in the xyz direction by the four longitudinal support members 53 and the piezo element 39.

  The lens holder 48 is sandwiched between a pair of magnetic circuits. Each magnetic circuit includes a magnet 55 facing the lens holder 48 and a metal plate 56 that supports the magnet 55, and is fixed on the actuator base 42. A pair of through-holes are formed in the lens holder 48, and the pair of through-holes are parallel to the coil central axis and the optical axis of the objective lens OB inside the focusing coil 50 of the lens holder 48 in the extending direction of the longitudinal support member 53. It is in a position to sandwich the objective lens OB. A yoke 57 extending from the metal plate 56 of the magnetic circuit is inserted into each through hole in a non-contact manner. Therefore, the focusing coil 50 and the tracking coil 51 are located in the magnetic gap of the magnetic circuit composed of the magnet 55 and the yoke 57.

  The focusing coil 50, the tracking coil 51, and the piezo element 39 are controlled by a focus servo circuit 29, an x-direction movement servo circuit 30x, and a y-direction movement servo circuit 30y, respectively. Since a parallel magnetic flux that is perpendicular to each coil can be generated in the magnetic gap, a driving force in the xz direction is generated by supplying a predetermined current to each coil, and the movable optical system described above is generated in each direction. Can be driven.

  In this way, the objective lens OB is driven in the x and y directions by using a voice coil motor, and the y direction is driven by the actuator base using a piezoelectric element or the like. In addition to this structure, the drive unit can use voice coil motors for all axes.

  A recording / reproducing method for recording or reproducing information by irradiating a hologram record carrier with a light beam using the hologram hologram apparatus will be described.

<Outline of hologram recording and reproduction>
At the time of hologram recording, as shown in FIG. 8, the coherent light of a predetermined intensity from the first laser light source LD1 is separated into a reference light beam and a signal light beam by the first half mirror prism HP1 (both beams are indicated by broken lines). For the sake of explanation of the optical path, it is shown shifted from the optical axis in FIG. 6).

  The signal light beam passes through the second half mirror prism HP2 and enters along the normal line of the reflection surface of the polarization spatial light modulator SLM. The signal light that has been modulated and reflected by the polarization spatial light modulator SLM is again incident on the second half mirror prism HP2, reflected, and travels toward the fourth half mirror prism HP4.

  The reference light beam is reflected by the third half mirror prism HP3 and travels toward the fourth half mirror prism HP4.

  The reference light and the signal light are merged by the fourth half mirror prism HP4 so as to be substantially coaxial and become the first light beam FB. The first light beam FB passes through the dichroic prism DP, is condensed on the hologram record carrier 2 by the objective lens OB, and a hologram is recorded.

  On the other hand, at the time of reproduction, as shown in FIG. 9, the light is separated into the reference light beam and the signal light beam by the first half mirror prism HP1 as in the recording, but the hologram is reproduced only by the reference light beam. By making the polarization spatial light modulator SLM non-reflective (transmission), only the reference light from the third half mirror prism HP3 passes through the dichroic prism DP and the objective lens OB as the first light beam FB, and the hologram Incident on the record carrier 2.

  The reproduction light (two-dot chain line) generated from the hologram record carrier 2 passes through the objective lens OB, the dichroic prism DP, the fourth half mirror prism HP4, and the third half mirror prism HP3, and enters the image detection sensor CMOS. The image detection sensor CMOS sends the output to the reproduction optical signal detection circuit 27, supplies the reproduction signal generated there to the control circuit 37, and reproduces the recorded page data. An imaging lens may be provided between the third half mirror prism HP3 and the image detection sensor CMOS.

  Here, positioning servo control with respect to the hologram disk 2 is performed by a servo beam during both hologram recording and reproduction. A triaxial actuator (objective lens driving unit 36) that can drive the objective lens in three axes in the x, y, and z directions with an error signal obtained by calculation based on the output of the photodetector PD by positioning servo control. To drive.

  As shown in FIGS. 8 and 9, the second laser light source LD2 for servo control emits a servo beam SB having a wavelength different from that of the first laser light source LD1. The servo beam SB (thin solid line) is used for servo detection of the second collimator lens CL2, the diffractive optical element GR, the polarization beam splitter PBS, and the quarter-wave plate 1 / 4λ as P-polarized light (bidirectional arrow indicating parallel to the paper surface). The light beam is guided to the optical path and merged substantially coaxially with the first light beam FB (signal light and reference light) by the dichroic prism DP immediately before the objective lens OB. The servo beam SB is reflected by the dichroic prism DP, then condensed by the objective lens OB, and enters the hologram record carrier 2. Reflected light from the hologram record carrier 2 (return light to the objective lens OB) passes through the quarter-wave plate 1 / 4λ and becomes S-polarized light (middle black wave line circle indicating perpendicular to the paper surface). It enters along the normal line of the light receiving surface of the servo photodetector PD through the ring lens AS.

  In addition, z-direction servo (focus servo) control includes the astigmatism method, the three-beam method, the spot size method, the push-pull method, etc. that are used in ordinary optical pickups. Can be used.

  For example, when the astigmatism method is used, one of the centers of the photodetector PD is composed of light receiving elements 1a to 1d having light receiving surfaces of four equal parts for receiving a beam as shown in FIG. The direction of the four dividing lines corresponds to the disk radial direction and the track tangential direction. The light detector PD is set so that the light spot at the time of focusing is a circle centered on the center of division of the light receiving elements 1a to 1d.

  The servo signal processing circuit 28 generates various signals according to the output signals of the light receiving elements 1a to 1d of the photodetector PD. If the output signals of the light receiving elements 1a to 1d are Aa to Ad in that order, the focus error signal FE is calculated as FE = (Aa + Ac) − (Ab + Ad), and the tracking error signal TE is TE = (Aa + Ad) − ( Ab + Ac). These signals are supplied to the control circuit 37.

<Details of recording and playback>
In the present embodiment, positioning servo control with the hologram record carrier 2 is always performed by the servo beam SB, and simultaneously, the hologram reproduction is performed by the first light beam FB (reference light) and the recording is performed by the first light beam FB (reference light and signal light). ).

  As shown in FIG. 11, the spot of the servo beam SB and the spot of the first light beam FB on the track of the reflective layer 5 are arranged substantially coincided during recording and reproduction.

  Hologram recording is performed by causing the reference light and signal light components of the first light beam FB to interfere in the hologram recording layer 7. Since the modulation signal (signal light component) modulated by the spatial light modulator SLM is a first-order or higher-order diffracted light component, it has a certain extent in the vicinity of the focused spot (Fourier plane). Therefore, most light rays are reflected on the reflective layer 5. On the other hand, since the reference light (or the 0th-order light component) is unmodulated DC light, it has a spot size determined by the numerical aperture and wavelength of the objective lens OB, and the perforated pinhole PH is somewhat larger than the spot size. If it is larger, the reference light is transmitted through the pinhole PH.

  As shown in FIG. 12, when recording a hologram, the reference light is transmitted through the pinhole PH. Therefore, in the hologram recording layer 7, interference between the incident reference light r and the incident signal light S, and the incident reference light r And interference of the reflected signal light RS occurs, and holograms A and B are formed based on the interference. Since the reference light r is transmitted as it is to the back side of the hologram record carrier 2, no hologram can be formed with the reflected reference light.

  As shown in FIG. 13, when reproducing a hologram, the reference light for reproduction is matched with the pinhole PH. By performing this operation, the reference light is transmitted to the back side of the hologram record carrier 2 through the pinhole PH. Since the reference light does not return to the objective lens OB side, the reference light does not return and enter the image detection sensor CMOS. For reproduction of the recorded hologram, a reproduction signal B is generated from the hologram B to the objective lens OB side by the reference light incident on the hologram record carrier 2. A reproduction signal A is generated from the hologram A on the side opposite to the objective lens OB. The reproduction signal A is reflected by the reflection layer 5 and returns to the objective lens OB side. Since the reproduction signals A and B are the same and overlap on the light receiving element, there is no particular problem.

<Hologram Apparatus of Other Embodiment>
In FIG. 14, hologram recording in a form in which reference light and signal light are not used separately for hologram recording / reproduction is performed, and a laser light source of another wavelength is used to control the relationship (focus, tracking) between the hologram record carrier and the pickup. An example of using the will be described.

  The hologram apparatus of FIG. 14 omits the first, second, and third half mirror prisms HP1, HP2 of the recording optical system, and includes the first laser light source LD1 and the first collimator lens CL1 at the position of the image detection sensor CMOS. The image detection sensor CMOS is disposed at the position of the two half mirror prisms HP2, and the transmissive spatial light modulator SLM is arranged between the fourth half mirror prism HP4 and the first collimator lens CL1 instead of the reflective spatial light modulator. 6 is the same as that shown in FIG. 6 except that the reproduced wave returning from the carrier via the objective lens OB is branched by the fourth half mirror prism HP4. The laser light from the first laser light source LD1 is converted into a parallel light beam by the collimator lens CL1, and then enters the transmissive spatial light modulator SLM. The spatial light modulator SLM has a function of electrically modulating a part of incident light electrically with a liquid crystal panel having electrodes divided in a matrix. The spatial light modulator SLM is used to modulate page data as an intensity distribution in the signal light beam. A light beam emitted from the spatial light modulator SLM becomes a first light beam FB including first-order or higher-order diffracted light (signal light component) and unmodulated zero-order light (reference light component). The first light beam FB of the signal light and the reference light is condensed on the hologram record carrier 2 by the objective lens OB and a hologram is recorded. That is, the hologram reproduction system includes a support unit that holds a hologram record carrier so as to be freely mounted, a light source that generates a coherent reference light beam, and a hologram record carrier according to recording information. An interference part that irradiates a reference light beam to the diffraction grating region formed inside the recording layer to generate a reproduction wave, and a return light and a reproduction wave that are reflected from the reflection layer of the reference light beam and return to the interference part. And a detection unit for detecting recording information imaged by the reproduction wave.

  In this reproducing operation, the first light beam FB consisting only of non-modulated laser light, that is, zero-order light (reference light component) is condensed on the hologram record carrier 2 via the objective lens OB by the transmissive spatial light modulator SLM. Then, the reproduction wave is reconstructed and returns to the pickup through the objective lens OB. The component reflected by the fourth half mirror prism HP4 enters the image detection sensor CMOS. The image detection sensor CMOS sends an output corresponding to the image formed by the reproduction light to the reproduction signal detection processing circuit 27 and supplies the reproduction signal generated there to the control circuit 50 to reproduce the recorded page data. To do. The configuration related to the servo beam SB (servo control) is the same as the configuration shown in FIG.

<Example 1>
As shown in FIG. 15, the pitches Px and Py of the pinhole PH of the reflective layer 5 are set as a predetermined distance determined from the multiplicity of the hologram HG recorded above the spot of the first light beam FB. The maximum multiplicity in an actual shift multiplex recording hologram system, that is, the value (number of times) indicating the maximum number of independent holograms that can be recorded in the same volume in the recording medium is as described above. Determined by configuration. The minimum pitch Px (that is, the minimum shift distance) is set by dividing the recorded hologram area by the maximum multiplicity. The pitch Px is set to be equal to or greater than the minimum shift distance.

  Positioning servo control with the hologram record carrier 2 is always performed by the servo beam SB, and at the same time, hologram recording is performed by the first light beam FB. Servo control can be performed by irradiating the adjacent pinhole PH with a plurality of servo beams.

<Example 2>
As shown in FIG. 16, when a track T equal to the hologram recording interval (Py) is provided between the pinhole PH mark rows (non-reflecting portion rows), the servo beam SB is 3 by a diffractive optical element such as a grating. As a beam, xy servo can be performed with two side beams and recording can be performed with a main beam. That is, the optical axis of the first light beam FB is arranged so that the first light beam FB is positioned at the center of the light spot of the three servo beams SB aligned on the straight line, and tracking servo control is performed, so Hologram recording is performed on the hologram recording layer 7 above the mirror surface.

<Example 3>
As shown in FIG. 17, a track T that is set to the hologram multiplexing interval Px in the x direction and extends in the y direction in the hologram multiplexing direction and a mark Y that coincides with the multiplexing interval Py in the y direction can be provided as a disc format. The track T of the reflective layer 5 is also set as a pitch Px as a predetermined distance determined from the multiplicity of the hologram HG recorded above the spot of the first light beam FB. As shown in the figure, the servo beam SB is divided into three beams by the grating during recording. The side beam is arranged on the track T so that the main beam in the center of the servo beam SB is arranged between the tracks T. Tracking servo control for causing the objective lens OB to follow the track T using a push-pull method or the like from the detection signal of the side beam is performed. The hologram record carrier 2 is moved by the interval Py in the y direction, and the spot of the first light beam FB is made to coincide with the pinhole PH.

  For the servo beam SB, in addition to the tracking servo control similar to that of the first embodiment, the time axis servo control for simultaneously tracking the objective lens OB in the y direction using the mark Y in the y direction is performed. Servo control by the servo beam SB is the same as in the first embodiment.

<Example 4>
The mark Y equal to the hologram recording interval in the extending direction on the track T of Example 3 shown in FIG. 17 has a shape in which a part of the group is interrupted. However, as shown in FIG. Can be formed such that a part of the track is inflated, or the mark Y2 can be formed such that a part of the track is notched.

<Example 5>
As shown in FIG. 19, tracks T1 and T2 adjacent in the x direction can be arranged so as to sandwich the row of pinholes PH arranged in the y direction. The missing part (mark Y) of the track T1 is set equal to the hologram recording interval. The track T2 is the same as that of the second embodiment shown in FIG. The track interval (Px) of the same type is set equal to the hologram recording interval.

<Example 6>
As shown in FIG. 20, the tracks T1 and T2 adjacent in the x direction can be arranged so as to sandwich the row of pinholes PH arranged in the y direction. The track T2 is a pit row or a mark row, and various information in addition to address information is recorded in advance. The track T1 is the same as that of the second embodiment shown in FIG. The track interval (Px) of the same type is set equal to the hologram recording interval.

  As described above, according to the present embodiment, since the reference light is always prevented from returning at the non-reflecting portion such as the pinhole PH of the reflective layer, the diffracted light from the reproduced hologram can be separated. Since only the reference light at the time of hologram recording is effectively made non-reflective, an extra hologram such as a reflected image is not recorded. As a result, the hologram recording layer is not deteriorated more than necessary. Further, since the reference light does not return to the detector side during reproduction, only the diffracted light from the hologram necessary for signal reproduction can be received. As a result, the reproduction SN is improved and stable reproduction can be performed.

  Further, in the above embodiment, the hologram record carrier disk 2 as shown in FIG. 21 is described as an example of the recording medium, but the shape of the hologram record carrier is not limited to a disc shape, for example, a plastic as shown in FIG. It may be a rectangular parallel flat optical card 20a made up of or the like. Also in such an optical card, the track may be formed in a spiral shape, a spiral arc shape or a concentric shape on the substrate, for example, with respect to the center of gravity, or the track may be formed in parallel on the substrate.

  Furthermore, in the above-described embodiment, hologram recording and mark recording are performed using the first beam FB and the servo beam SB (second beam) having different wavelengths from the first and second laser light sources LD1 and LD2. Although the case where the servo control of the light beam is executed has been described, the first and second laser light sources LD1 and LD2 may emit laser light having the same wavelength. In this case, for example, the first beam FB is turned on only in a time zone that requires hologram recording while performing servo control while suppressing the light intensity of the servo beam SB to a level that does not lead to hologram recording.

1 is a schematic partial sectional view showing a hologram record carrier according to an embodiment of the present invention. FIG. 5 is a schematic partial sectional view showing a hologram record carrier of another embodiment according to the present invention. FIG. 6 is a schematic partial perspective view showing a hologram record carrier of another embodiment according to the present invention. The block diagram which shows schematic structure of the hologram apparatus which records or reproduces | regenerates the information of the hologram record carrier of embodiment by this invention. The schematic perspective view which shows the outline of the pick-up of the hologram apparatus which records and reproduces | regenerates the information of the hologram record carrier of embodiment by this invention. The block diagram which shows the outline of the pick-up of the hologram apparatus which records / reproduces the information of the hologram record carrier of embodiment by this invention. The schematic perspective view which shows the outline of the triaxial actuator for the objective lens in the pick-up of the hologram apparatus which records / reproduces the information of the hologram record carrier of embodiment by this invention. The block diagram which shows the outline of the pick-up of the hologram apparatus which records / reproduces the information of the hologram record carrier of embodiment by this invention. The block diagram which shows the outline of the pick-up of the hologram apparatus which records / reproduces the information of the hologram record carrier of embodiment by this invention. The top view which shows a part of photodetector in the pickup of the hologram apparatus which records and reproduces | regenerates the information of the hologram record carrier of embodiment by this invention. FIG. 3 is a schematic partial cross-sectional view illustrating recording / reproduction of a hologram record carrier according to an embodiment of the present invention. FIG. 3 is a schematic partial cross-sectional view illustrating a recording process of a hologram record carrier according to an embodiment of the present invention. FIG. 4 is a schematic partial cross-sectional view illustrating a reproducing process of the hologram record carrier according to the embodiment of the present invention. The block diagram which shows the hologram apparatus of other embodiment by this invention. The top view which shows the track structure of the hologram recording carrier of other embodiment by this invention. The top view which shows the track structure of the hologram recording carrier of other embodiment by this invention. The top view which shows the track structure of the hologram recording carrier of other embodiment by this invention. The top view which shows the track structure of the hologram recording carrier of other embodiment by this invention. The top view which shows the track structure of the hologram recording carrier of other embodiment by this invention. The top view which shows the track structure of the hologram recording carrier of other embodiment by this invention. The perspective view which shows the hologram record carrier of embodiment by this invention. The perspective view which shows the perspective view which shows the hologram optical card of other embodiment by this invention.

Explanation of symbols

2 ... Hologram record carrier 3 ... Substrate 5 ... Reflective layer 6 ... Separation layer 7 ... Hologram recording layer 8 ... Protective layer 20a ... Optical card 22 ... Spindle motor 23 ... Pickup 24 ... Pickup drive unit 25a ... First light source drive circuit 25b ... Second light source drive circuit 26 ... Spatial light modulator drive circuit 27 ... Reproduction optical signal detection circuit 28 ... Servo signal processing circuit 29 ... Focus servo circuit 30x ... x-direction movement servo circuit 30y ... y-direction movement servo circuit 31 ... Pickup position detection Circuit 32 ... Slider servo circuit 33 ... Rotation speed detection unit 34 ... Rotation position detection circuit 35 ... Spindle servo circuit 36 ... Object lens drive unit 37 ... Control circuit 38 ... Support unit 39 ... Piezo element 42 ... Actuator base 42c ... Opening 45 ... Rise prism 48 ... Lens holder 50 ... Focusing coil 51 ... Track Coil 53 ... Longitudinal support member 42a ... Overhang 55 ... Magnet 56 ... Metal plate 57 ... Yoke HG ... Hologram T ... Track FB ... First light beam SB ... Second light beam, servo beam PH ... Pinhole (non-reflective portion) )
Y ... y-direction positioning mark LD1 ... first laser light source CL1 ... first collimator lens HP1 ... first half mirror prism SLM ... polarization spatial light modulator HP2 ... second half mirror prism HP3 ... third half mirror prism HP4 ... fourth Half mirror prism CMOS ... image detection sensor LD2 ... second laser light source CL2 ... second collimator lens PBS ... polarization beam splitter 1/4? ... quarter wave plate AS ... coupling lens PD ... photodetector DP ... dichroic prism OB ... Objective lens

Claims (9)

A hologram record carrier on which information is recorded or reproduced by light irradiation,
A hologram recording layer that stores therein an optical interference pattern by a component of coherent reference light and signal light as a diffraction grating;
A reflective layer laminated on the opposite side of the hologram recording layer from the light incident side;
A hologram record carrier comprising: a plurality of non-reflective portions arranged on the reflective layer at equal intervals to the recording interval of the diffraction grating.   The hologram record carrier according to claim 1, wherein the non-reflective portion is a pinhole.   The hologram record carrier according to claim 1, wherein the non-reflective portion has a transmittance with a characteristic value higher than the transmittance of the reflective layer.   2. The hologram record carrier according to claim 1, wherein the non-reflecting portion has an absorptance having a characteristic value higher than that of the reflecting layer.   2. The hologram record carrier according to claim 1, wherein the non-reflecting portion has a reflectance having a characteristic value lower than that of the reflecting layer.   The hologram record carrier according to any one of claims 3 to 5, wherein the characteristic value of the non-reflective portion is a wavelength of the coherent reference light and signal light.   The reflection layer has a track extending from each of the objective lenses so as to follow a spot of a light beam focused through the hologram recording layer and the reflection layer without extending apart from each other. The hologram record carrier according to any one of claims 1 to 6.   8. The hologram record carrier according to claim 7, wherein the track is formed in a spiral shape, a spiral arc shape or a concentric circle shape. 9. The hologram record carrier according to claim 7, wherein the tracks are formed in parallel.

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